Theoretical investigation of the AlN (0 0 0 1)-(2 × 2) surface doped with nickel: Structural, electronic and magnetic properties

Abstract

Structural, electronic and magnetic properties of the nickel doped AlN (0 0 0 1)-(2 × 2) surfaces are investigated by spin-polarized first-principle total-energy calculations. The exchange–correlation potential energies are treated within the generalized gradient approximation (GGA) with the Perdew, Burke and Enzernof (PBE) functional. Electron-ion interactions are dealt with the pseudopotential approach. According to results the H3 site is the most favorable structure in the adsorption of Ni at different coverage from ¼ to 1 monolayer (ML). When coverage is in the range from ½ to 1 ML, we found ferromagnetic (FM) behavior as a consequence of the Ni presence with magnetic moment (>0.7 μB/atom). Also, we found the formation of dimers, trimers and atomic chains in the ½, ¾ and 1ML coverage, respectively. The minimum energy pathways in the Ni adsorption and incorporation show activation energies of 1.53 and 1.26 eV, respectively. The deposit of Ni into substitutional sites suggests the possibility of growing NiN epitaxially. We employed the surface formation energy formalism to investigate the different structures stability. Results indicate that the Ni doping is favorable under Ni-rich conditions in all the range of chemical potential ΔμAlN, finding four AlN surfaces with different magnetic properties: the 1Ni ads and 4Ni subs models are non-magnetic, however the 1Ni subs model is FM and the 2Ni subs model is antiferromagnetic (AFM) with magnetic moments of the order of 0.8 μB/atom. Therefore, we can conclude that high concentrations of Ni induce a non-magnetic behavior, and low concentrations favor the magnetic properties, provided that the Ni atoms occupy substitutional sites. The density of states shows that only the 1st ML of surfaces is metallic, in contrast layers beneath the first layer are semiconductor, where the valence and conductions bands are mainly formed by the N-p and Al-p orbitals, respectively.